The broad, long-term objective of this proposal is to further our understanding of the pathogenesis of Lyme neuroborreliosis. We have established that live Borrelia burgdorferi spirochetes elicit inflammatory mediators from microglia and astrocytes. When B. burgdorferi penetrate brain tissue cultured ex vivo, glial cells produce inflammatory mediators and, concomitantly, oligodendrocytes and neurons undergo apoptosis. We have further determined, in rhesus macaques with Lyme meningitis due to intrathecal B. burgdorferi inoculations, that neurons and glia in dorsal root ganglia also undergo apoptosis. We have shown, moreover, that spirochetes co-cultured in vitro with neurons alone fail to elicit neuronal apoptosis but when microglia are present in the cultures neuronal apoptosis readily occurs. Astrocytes do no exert this effect. Microglia, in contrast to neurons or astrocytes, release very large amounts of inflammatory mediators when exposed to B. burgdorferi in vitro. A predominant mediator released by microglia in vitro and into the cerebrospinal fluid of rhesus macaques with Lyme meningitis is the chemokine C-C motif ligand 2 (CCL2, aka MCP-1). While these findings suggest that inflammation is required to elicit apoptosis of neurons and glial cells, a causal relationship between these two phenomena has not been demonstrated in Lyme neuroborreliosis. In addition, the mechanism whereby spirochetes activate microglia has not been examined in full. Thus far we have demonstrated that the adaptor molecule myeloid differentiation primary response gene 88 (MyD88), and the receptors Toll-like receptor 1 (TLR1), and TLR2 are directly involved in the activation of macrophage/monocytes by live B. burgdorferi, and that these TLR are expressed, and their expression is up-regulated, in primary rhesus microglia. We have also shown that MyD88 is involved in the response of microglia to B. burgdorferi. To move the field forward in the direction prescribed by these findings we propose to evaluate the following hypotheses: Specific aim 1) inflammation is required for B. burgdorferi to cause neuronal and oligodendrocyte apoptosis. Specific aim 2) as with neurons, microglia are necessary and sufficient as a source of the inflammatory response that causes apoptosis of oligodendrocytes. Specific aim 3) a. the inflammatory response to live B. burgdorferi in microglia involves the TLR pathway; b. CCL2 is a key player in this process. We plan to address these goals with experiments in vitro, ex vivo, and in vivo, using the rhesus monkey model of Lyme disease.